JP2634547B2 - Injection mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding die for molding a resin product having a variable thickness so as to suppress molding defects such as sink marks and warpage.

[0002]

2. Description of the Related Art Conventionally, an injection molded article such as a bumper of a vehicle made of a resin is usually formed into a fixed thickness as shown in Japanese Utility Model Application Laid-Open No. 62-119213. However, recently, the necessity of reducing the weight of a vehicle body has been avoided in order to improve fuel efficiency, and reduction of the weight of a bumper has been regarded as important as one of the measures.

[0003]

However, the bumper plays a large role as a design part in addition to its original purpose such as protecting other functional parts in the event of a collision, and simply reduces the thickness of an arbitrary part. With only the above, there is a problem that, for example, the impact absorption function, heat resistance, and the like are impaired, or the filling is insufficient at the time of molding and the appearance is impaired. In order to reduce the weight without impairing the original function of the bumper and the design effect,
The lower part of the bumper is made thinner than the upper part, and a gradually changing part is provided between the relatively thick part of the upper part and the thin part of the lower part to gradually change the thickness to reduce sink marks, warpage, deformation, etc. We have devised a bumper structure that maintains the appearance quality while avoiding molding defects and ensures the necessary rigidity. However, if a gradual change portion is provided between the thick portion and the thin portion to avoid a rapid change in the thickness as described above, it is effective to suppress the occurrence of molding failure, but the gradual change portion is simply used. Various experiments have shown that the effect of suppressing the occurrence of molding defects cannot be maximized by simply providing it, and the degree of the effect depends on the rate of wall thickness change, the gradual change range, and the resin injection direction. The result became clear.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a thick cavity portion forming a relatively thick thick portion, a thin cavity portion forming a relatively thin thick portion,
In an injection mold having a gradually changing cavity portion whose thickness gradually changes from the thick cavity portion toward the thin cavity portion, a gate portion for resin injection is provided in the thick cavity portion, and the thick cavity portion is provided. And the thickness change rate of the thin cavity portion was set to 35% or less, and the length of the gradually changing cavity portion was set to 50 mm or more. Here, the thickness change rate is a value represented by {(ac) / a} × 100%, where a is the thickness of the thick cavity portion and c is the thickness of the thin cavity portion. The length of the gradually changing cavity is the length of the gradually changing cavity in the direction connecting the thick cavity and the thin cavity.

[0005]

First, the resin filling direction is set to the direction from the thick cavity to the thin cavity to prevent molding failure due to insufficient pressure. In other words, conversely, if filling is performed from the thin cavity to the thick cavity, the resin that has greatly lost the resin pressure in the thin cavity enters the thick cavity and the resin can sufficiently adhere to the mold surface. This leads to molding failure. Next, if the thickness change rate is set to 35% or less, and the degree of change in the thickness is reduced to such an extent that the length of the gradually changing cavity portion is set to 50 mm or more, molding failure does not occur.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the injection mold according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of an injection mold,
FIG. 2 is a perspective view of a bumper as an example of a molded product, and FIG.
FIG. 4 is a sectional view taken along the line AA of FIG. 4, and FIG. 4 is an explanatory view for explaining the principle of the gradually changing wall thickness plan.
Shows a plan with a step-like thickness change.

The injection mold according to the present invention is, for example, shown in FIGS.
The bumper 1 is configured as an injection mold for molding a resin bumper 1 made of a resin as shown in FIG. 1, and the bumper 1 is located above when mounted on a vehicle body and projects substantially horizontally outward from the vehicle body side. 1a, a vertical surface portion 1b extending downward from the upper surface portion 1a, a lower surface inclined portion 1c bent obliquely downward from the lower end of the vertical surface portion 1b toward the vehicle body, and further downward from the lower surface inclined portion 1c. After extension, a corner portion 1d is turned back toward the vehicle body.

The thickness of the bumper 1 is partially reduced for weight reduction, that is, the upper surface 1a and the vertical surface 1a.
b is a relatively thick thick portion A, the lower corner portion 1d is a relatively thin thin portion C, and the middle, inconspicuous lower surface inclined portion B is formed at a constant ratio. Are gradually changed. For example, the thick part A has a thickness of about 3.8 mm, and the thin part C has a thickness of, for example, 2.8 mm.
About. Incidentally, the broken line portion in FIG. 2 is the center line of the gradually changing portion B.

As shown in FIG. 1, the injection mold 2 includes a fixed mold 3 and a movable mold 4 which form a cavity 5 having the same shape as the shape of the bumper 1. It extends vertically.

At one end of the cavity 5, a thin strip-shaped film gate 6 for simultaneously injecting resin from the longitudinal direction of the bumper 1 is provided. A runner 7 is provided. A sprue 8 is connected to a substantially central portion in the longitudinal direction of the film gate runner 7 and is connected to a hot runner 9.

The tip of an extrusion pin 11 for projecting a product after opening the mold faces the cavity 5 or the film gate runner 7, and the base end of the extrusion pin 11 advances and retreats to the movable mold 4 side. Extruded plate 1 movably provided
2 is fixed.

The push plate 12 is provided with a return pin 13 for returning to the original position.
Biased backwards by

The cavity 5 has a thick portion A of the bumper 1.
5A, a gradually changing cavity 5B corresponding to the gradually changing portion B, and a thin cavity 5C corresponding to the thin portion C.

The film gate 6 is provided on the side of the thick cavity 5A, so that the resin is filled from the gradually changing cavity 5B into the thin cavity 5C through the thick cavity 5A. By the way, as shown in FIGS. 2 and 3, the bumper 1 immediately after molding has a film gate portion 1 in which the resin in the film gate 6 has solidified.
e and the film gate runner portion 1f in which the resin in the film gate runner 7 is solidified are integrally formed. The film gate 1e and the film gate runner 1f
Are then cut and discarded.

Here, the reason why the gradually changing cavity structure is adopted is that when forming by a stepwise thickness change as shown in FIG. While the difference in the amount of shrinkage is large and large stress is generated at the boundary, deformation, deformation and other appearance defects are likely to occur,
This is because, in the case of the gradually changing thickness scheme shown in (a), the difference in the maximum shrinkage amount is small, the generated stress is also small, and the appearance defect is unlikely to occur.

That is, while the resin continues to shrink during cooling and solidification, the thicker part generally has a longer solidification time and tends to increase the shrinkage, and the thinner part has a shorter solidification time and the shrinkage is small. Tend to be. Therefore, by gradually changing the thickness, the locally generated stress can be suppressed low, and the deformation and the like are reduced.

In the case of the present invention, for example, the thickness of the thick cavity portion 5A is defined as a, and the thickness of the thin cavity portion 5C is defined as c.
(The thicknesses corresponding to the thicknesses a and c of the molded body in FIG. 4 respectively), the thickness change rate represented by {(ac) / a} × 100% is set to 35% or less, and Strange cavity 5B
(The value corresponding to r in FIG. 4A) is 50 mm or more.

This is based on an experimental result as shown in FIG. FIG. 5 is a data table obtained by experimenting the state of occurrence of deformation and the like when molding was performed by changing the combination of the length of the gradually changing cavity portion and the rate of change in thickness, and the vertical column shows the thickness change rate (thickness change rate). )%, And the horizontal column shows the gradually changing length (length of the gradually changing cavity portion) mm.

As is apparent from the experimental data, if the thickness change rate (thickness change rate) is 35% or more, even if the length of the gradually changing portion B (slowly changing cavity portion 5B) is 80 mm, molding failure is not caused. If the length of the gradually changing portion B (gradually changing cavity portion 5B) is set to 50 mm or less, the thickness change rate (thickness change rate) may be set to a small value such as 10%. It is also found that there is a possibility that molding failure may occur.

Therefore, in the case of the present invention, the thick cavity 5
By setting the thickness a of A to 3.8 mm and the thickness c of the thin cavity portion 5C to 2.8 mm, the thickness change rate of the cavity 5 is kept within 35%, and the length of the gradually changing cavity portion 5B is set to 5%.
0 mm. And the bumper 1 with little deformation can be molded by such a configuration, and the weight can be reduced without deteriorating the commercial value.

By the way, it has also been found that the following effects can be obtained secondarily by such a configuration.

In other words, it is generally said that when the pressure in the cavity 5 is insufficient, the resin cannot spread all over the cavity and deformation tends to occur. When the molding pressure is increased, shrinkage is reduced. I have. on the other hand,
The pressure in the cavity 5 decreases as the distance from the film gate 5e increases, and in the case of the embodiment, the pressure on the upper surface 1a side of the bumper 1 is high, and the pressure decreases on the corner portion 1d side, so that a difference in the contraction rate is likely to occur. .

However, in the present invention, since the corner portion 1d side is formed as the thin portion C, the shrinkage is reduced by the reduced thickness, and the effect of the pressure drop and the effect of the thinning are offset, resulting in FIG. Thus, it was confirmed that the difference in shrinkage ratio became small.

That is, FIG. 6 shows a test piece 20 having a thick portion A 3.8 mm, a gradually changing portion B whose thickness changes linearly, and a thin portion C 2.8 mm as shown in FIG. B)
As shown in the table, the length of the gradually changing cavity portion 5B corresponding to the length r of the gradually changing portion B is changed from 0 to 80 mm so that the contraction rate of the width P of the thick portion A and the width Q of the thin portion C are changed. Was measured and the difference was determined.

As a result, it can be seen that the difference in shrinkage ratio is smaller in any of the molding materials X, Y, and Z than in the case of a constant thickness product. Therefore, according to the present invention, it is effective in reducing the influence of deformation due to the difference in shrinkage ratio.

[0026]

As described above, according to the injection mold of the present invention, the thickness change rate of the thick cavity portion and the thin cavity portion is 35%.
% And the length of the gradually changing cavity portion is set to 50 mm or more to suppress the occurrence of deformation and the like.
Molding can be performed in a state where molding material is saved without deteriorating appearance quality. Also, by providing a gate in the thick cavity portion and injecting the resin from the thick cavity portion side to the thin cavity portion side, there is a problem that the resin is injected from the opposite thin cavity portion side, that is, in the thin cavity portion, There is no problem that the resin with a large pressure loss enters the thick cavity portion and cannot be brought into close contact with the mold, and it is unlikely to cause problems such as insufficient filling and insufficient pressure. Further, by setting the thin portion having a small shrinkage ratio as the downstream side of the resin filling, a difference in shrinkage ratio between the upstream side and the downstream side is reduced, and the degree of deformation caused by the difference in shrinkage ratio can be reduced. Effects can also be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an injection mold.

FIG. 2 is a perspective view of a bumper as an example of a molded product.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIGS. 4A and 4B are explanatory diagrams for explaining the principle of a gradually changing thickness plan, wherein FIG. 4A shows a gradually changing thickness plan, and FIG.

FIG. 5 is an example of a data table for experimenting on the occurrence state of deformation and the like when molding is performed by changing the combination of the length and the rate of change of the thickness of the gradually changing cavity portion.

FIG. 6 shows experimental data of a difference in shrinkage ratio between a thick portion and a thin portion of a test piece, where (a) is a test piece and (b) is an example of a data table.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bumper 2 Injection mold 5 Cavity 5A Thick cavity part 5B Gradual change cavity part 5C Thin cavity part 6 Film gate

Claims (1)

(57) [Claims] 1. A thick cavity portion forming a relatively thick thick portion, a thin cavity portion forming a relatively thin thin portion, and from the thick cavity portion to the thin cavity portion. In the injection mold having a gradually changing cavity portion whose thickness gradually changes, a gate portion for resin injection is provided in the thick cavity portion, and the thickness change rate of the thick cavity portion and the thin cavity portion is 35%. An injection mold characterized in that the length is set within 50 mm and the length of the gradually changing cavity is 50 mm or more.